From: Арсений <a@saur0n.science>
To: "Rich Felker" <dalias@libc.org>
Cc: musl@lists.openwall.com, jwakely@redhat.com,
"Florian Weimer" <fw@deneb.enyo.de>
Subject: Re[2]: [musl] Mutexes are not unlocking
Date: Sun, 22 Nov 2020 22:45:44 +0300 [thread overview]
Message-ID: <1606074344.985184902@f157.i.mail.ru> (raw)
In-Reply-To: <20201122192824.GQ534@brightrain.aerifal.cx>
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Hello,
Yes, it is inlined:
0x00007ffff7e0e3e9 <+88>: mov 0x3b98(%rip),%r12 # 0x7ffff7e11f88
0x00007ffff7e0e3f0 <+95>: test %r12,%r12
0x00007ffff7e0e3f3 <+98>: je 0x7ffff7e0e3fd <testMutexPP(std::mutex&, char const*)+108>
0x00007ffff7e0e3f5 <+100>: mov %rbp,%rdi
0x00007ffff7e0e3f8 <+103>: callq 0x7ffff7e0d270 <pthread_mutex_unlock@plt>
Weak reference to pthread_key_create() is stored at 0x7ffff7e11f88. On musl, this memory location contains 0x0.
>Воскресенье, 22 ноября 2020, 22:28 +03:00 от Rich Felker <dalias@libc.org>:
>
>On Sun, Nov 22, 2020 at 08:23:23PM +0100, Florian Weimer wrote:
>> * Rich Felker:
>>
>> > On Sun, Nov 22, 2020 at 09:43:35PM +0300, Арсений wrote:
>> >>
>> >> Hello,
>> >> The problem is that mutex is not got unlocked after the first unlock().
>> >>
>> >> libstdc++ uses a wrapper for pthread called gthreads. This wrapper
>> >> checks for the state of the mutex system. For
>> >> example, pthread_mutex_unlock() is called in a following way:
>> >>
>> >> static inline int
>> >> __gthread_mutex_unlock (__gthread_mutex_t *__mutex)
>> >> {
>> >> if (__gthread_active_p ())
>> >> return __gthrw_(pthread_mutex_unlock) (__mutex);
>> >> else
>> >> return 0;
>> >> }
>> >
>> > Yes. This code is invalid (it misinterprets weak symbol information to
>> > draw incorrect conclusions about whether threads may be in use) and
>> > thus is disabled in builds of gcc/libstdc++ targeting musl-based
>> > systems. GCC and glibc-based distro folks mostly don't care because
>> > it only breaks static linking, but some of them actually hack gcc's
>> > libpthread.a into one giant .o file to work around the problem rather
>> > than fixing this in gcc...
>>
>> GCC 11 has a fix (if used along with glibc 2.32), but I wonder if it's
>> going to run into a similar issue because inlined code from older GCC
>> versions uses a diverging version of the check.
>>
>> Jonathan, more context is here:
>>
>> < https://www.openwall.com/lists/musl/2020/11/22/1 >
>Uhg, that's a really nasty problem. Is __gthread_active_p() also
>inlined? Or can it be given a definition to mitigate the problem?
>
>Rich
——
Арсений
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next prev parent reply other threads:[~2020-11-22 19:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 5:25 a
2020-11-20 5:58 ` Rich Felker
2020-11-21 6:46 ` Re[2]: " a
2020-11-21 15:51 ` Rich Felker
2020-11-22 18:43 ` Re[2]: " Арсений
2020-11-22 19:11 ` Rich Felker
2020-11-22 19:23 ` Florian Weimer
2020-11-22 19:28 ` Rich Felker
2020-11-22 19:45 ` Арсений [this message]
2020-11-22 20:05 ` Re[2]: " Арсений
2020-11-23 12:24 ` Jonathan Wakely
2020-11-23 14:56 ` Rich Felker
2020-11-23 16:58 ` Jonathan Wakely
2020-11-23 11:41 ` Jonathan Wakely
2020-11-23 14:53 ` Rich Felker
2020-11-23 16:19 ` Jonathan Wakely
2020-11-23 16:51 ` Rich Felker
2020-11-23 17:10 ` Jonathan Wakely
2020-11-23 17:18 ` Florian Weimer
2020-11-23 16:59 ` Florian Weimer
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